[PIG-1876] Typed map for Pig

• Type: New Feature
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 0.9.0
• Component/s: impl
• Hadoop Flags: Reviewed

Release Note

User can specify the a typed map in place of untyped map using the syntax:
map[type]

Untyped map still works as before.

• Assignee: Daniel Dai
• Reporter: Daniel Dai
• Created: 01/Mar/11 23:54
• Updated: 26/Sep/13 04:54
• Resolved: 09/Mar/11 22:52

Description

Currently Pig map type is untyped, which means map value is always of bytearray(ie. unknown) type. In PIG-1277, we allow unknown type to be a shuffle key, which somewhat relieve the problem. However, typed map is still beneficial in that:

1. User can make semantic use of the map value type. Currently, user need to explicitly cast map value, which is ugly
2. Though PIG-1277 allow unknown type be a shuffle key, the performance suffers. We don't have a raw comparator for the unknown type, instead, we need to instantiate the value object and invoke its comparator

Here is proposed syntax for typed map:
map[type]

Typed map can be used in place of untyped map could occur. For example:
a = load '1.txt' as(map[int]);
b = foreach a generate (map[(i:int)])a0; - - Map value is tuple
b = stream a through `cat` as (m:map[

{(i:int,j:chararray)}

]); - - Map value is bag

MapLookup a typed map will result datatype of map value.
a = load '1.txt' as(map[int]);
b = foreach a generate $0#'key';

Schema for b:
b:

{int}

The behavior of untyped map will remain the same.

Issue Links

• relates to: PIG-3485 Remove CastUtils.bytesToMap(byte[] b) method from LoadCaster interface